Generally, a thermostat is arranged for cooling-water circulation passages in a cooling system for an engine of a vehicle. When a temperature of cooling water is low at cold startup, the thermostat operates to close a water passage for circulation of cooling water between the engine and a radiator and open a water passage for return of the cooling water from the engine to the engine without via the radiator, whereby the cooling water is circulated without passing through the radiator to prioritize warming of the engine.
As is old and well-known, this kind of thermostat operates on a mechanical basis such that increase in temperature of the cooling water dissolves and increases in volume of wax enclosed in a casing, which triggers a needle, a spring or the like to open a valve.
There is, for example, the following Patent Literature 1 as a related art literature pertinent to such kind of cooling system for an engine.